Resonant and semi-resonant DC-DC converters, including isolated and non-isolated topologies, are used in a variety of applications such as telecommunications, processors, etc. because of their zero-voltage (current) switching characteristic and their ability to utilize parasitic components. Among numerous topologies, the semi-resonant converter with transformer/tapped-inductor is an attractive topology for high voltage conversion ratio without isolation. Lower cost and higher efficiency are the main advantages of such converters over other solutions.
The output current of many resonant and semi-resonant DC-DC converters has a half cycle sinusodial-like shape each switching cycle. A classic example of such a sinusodial-like output current occurs in discontinuous conduction mode (DCM) in which current through the output inductor falls to zero during part of the switching period. Many resonant and semi-resonant DC-DC converters also have a variable switching frequency such that the switching period can vary from cycle to cycle. For these types of resonant and semi-resonant converters with sinusodial-like output current and variable switching frequency, it is difficult to obtain the cycle average value of the output current which is equal to the load current in semi-resonant converters. The cycle average is used for adaptive voltage positioning (AVP), phase current balancing and phase dropping/adding in multi-phase systems. Because of the sinusodial-like shape of the output current, conventional low pass filtering techniques for obtaining the cycle average value of the output current are not adequate, since very low bandwidth filters would be needed for obtaining the average value of the output current. Very low bandwidth filters add latency to the control loop and may degrade the transient performance of the converter. In addition, very low bandwidth filters yield an inaccurate total current which is obtained by summing the filtered values in each channel, especially at higher load frequency transients. Also, very low bandwidth filters are not suitable for use in peak current limit control or other control mechanisms utilizing the current information, nor are they suitable for use in current balancing/sharing control.
As such, there is a need for an improved technique for obtaining the cycle average value of output current for resonant and semi-resonant DC-DC converters having a variable switching frequency and output current having a sinusodial-like shape.